Product of intelligent sweeping robot surface shell is shown in Figure 1. Maximum size of product is 384.90 mm * ø316.00mm * 130.80 mm, average thickness of plastic part is 2.00 mm, material of plastic part is PP, shrinkage rate is 1.018, and weight of plastic part is 512.64 gram. Technical requirements for plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.

 

Figure 1 Product picture of intelligent sweeping robot surface shell
It can be seen from Figure 1 that structure of plastic part is a closed shell, and appearance is like a peach. Top surface of plastic part has bone position, column position, convex shape and groove. Round bones on the back of plastic part form a deep wall, and there are multiple deep ribs along circumference. There are also multiple bone positions in the center of inner top. Therefore, difficulty of mold design lies in ejection of plastic part.

 

Mold design cavity ranking is 2 cavities. Mold design drawing is shown in Figure 2. Due to large size of plastic part itself, mold is a large mold with 2 cavities. Mold gating system adopts a hot runner system and is a large mold at the same time. Mold base is a non-standard mold base with a size of 75108. Mold cores of two cavities are designed separately, which is convenient to separate two machine tools for processing at the same time.
Four corners of mold core are positioned between front and rear mold cores to facilitate accurate mold clamping. Due to large size of mold core, deep cavity and depth of fine frame, lower frame of mold core and matching of frame are more difficult, so on two sides of mold core away from reference angle, inclination of 3 ゜ is designed to cooperate with fine frame of front and rear molds. Cancel slope at matching mouth of die core and fine frame. Purpose of this is to facilitate machining of die core by using vertical edge as machining reference, such as centering of die core during EDM. Six locking blocks 13 are designed on the edge of mold base B board, and milling grooves are fixed on B board with screws. Locking block 13 is matched with wear-resistant plate on inclined surface of A plate at an 8 ゜ inclined surface.

 

Plastic part is a large-size deep-cylinder plastic part, and back mold has a deep bone position, which makes it difficult to eject plastic part. Especially semi-circular deep wall bone position has greater tightening force on back mold. Material of plastic part is PP. This material has poor rigidity. When packing force is large, it is easy to cause whitening or top-through, and it may also cause large deformation of plastic part. In summary, if ejector pin is directly designed to eject, plastic part cannot be ejected effectively.
Under normal circumstances, ejection of plastic parts from mold, whether it is a single or multi-element ejection mechanism, ejection action is completed at one time. However, due to special shape of plastic part or need for production automation, if plastic part is difficult to be removed from mold cavity or poor demolding is caused by a single ejection action, it is necessary to add another ejection action to successfully eject plastic part. out. For plastic parts with thin walls and deep cavities or complex shapes, sometimes in order to avoid excessive stress on plastic parts once ejected, a second ejection is also used to disperse ejection force and ensure quality of plastic parts. According to above analysis, this set of mold plastic parts must be ejected twice. Secondary ejection mechanism is usually that part or all of demolding components are first released from plastic part together, then some of ejected components are stopped while the other part of components continue to be ejected from plastic part.

 

There are many mechanisms for secondary ejection. One commonly used in Europe is HASCO standard secondary ejection component Z169. Its specifications are shown in Figure 4. Customer for this set of molds is an Italian customer, and Z169/40 is selected for secondary ejection. It is divided into two layers. Upper side is designed with push block and thimble, bottom of thimble board is designed with straight top and thimble. When ejecting, first two layers of ejector plates act at the same time to demold parts that are difficult to demold, then center ejector pin ejects upper ejector plates to achieve demoulding of plastic parts.
Secondary ejector mechanism of HASCO adopts mechanical action to eject, which is reliable in operation and long in service life. Regardless of size of mold, a secondary ejection device is designed and designed in the center of mold.

 

 

Figure 2 Mold diagram of face shell of intelligent sweeping robot

 

Figure 3 3D drawing of mold

 

 

 

Figure 4 HASCO secondary ejection device Z169 size parameters